1. Field of the Invention
The present invention is generally directed to a liquid administration system and more particularly to an apparatus for administering parenteral liquids from a supply container to a patient, wherein the flow rate is maintained at a constant value without regard to the amount of liquid remaining in the supply container or to changes in pressure exerted on the apparatus.
2. Description of the Prior Art
In the medical practice, it is often necessary to intravenously feed a patient with parenteral liquids, such as blood, plasma, dextrose solutions or the like. Such infusions are customarily carried out by employing intravenous (IV) kits incorporating a supply bottle or other container of liquids suspended above the patient and having a drop counting or drip chamber facilitating the determination of the drip rate therethrough, a drip tube through which the liquid to be infused flows by gravity feed, and an administering needle connected to the drip tube. The infusion rate is controlled in the drip chamber by means of a flow controller such as a pinch clip. When infusions are carried out, the drip tube and needle are initially purged of air, the needle is inserted into a vein, and the flow controller compresses the drip tube to restrict the initial flow of liquid. The number of drops falling through the drip chamber are determined by trial and error adjustment of the flow controller.
A major disadvantage encountered with this type of system is a variation that often takes place in the rate of liquid flow. In this system, a pinch clip is customarily placed under the supply bottle for convenience of operation. As the liquid level in the supply bottle falls, the hydrostatic head pressure providing the driving force for flow through the drip tube decreases. The term "hydrostatic head pressure", as used herein, means the pressure differential resulting from the vertical distance separating the two levels of liquid, in this case the liquid level in the supply container and the liquid level at the point of entry into the patient. Changes in hydrostatic head pressure often result in a substantial fluctuation in the volume of liquid being administered to the patient. The flow rate changes can be caused by situations such as changes in blood pressure, a patient voluntarily or involuntarily raising or lowering his infusion arm, partial clogging of the administering needle and dislodging of the administering needle. If the supply bottle drains itself of liquid, it is also possible to get air into the patient which is a dangerous condition to health. All of these conditions result in a time-consuming depletion of a technician's or nurse's time.
There are many teachings in the art of active complex metering devices intended to provide volumetric, or accurately measured volume per unit time, metering of fluids into the patient. Such active systems are usually complex and costly.
There are a variety of prior art references disclosing systems for administering parenteral liquids. U.S. Pat. No. 3,941,126 to Dietrich, et al. and U.S. Pat. No. 4,191,183 to Mendelson disclose the general concept of multiple intravenous feed lines from multiple supply containers which discharge into a common single chamber and then proceed to the patient. U.S. Pat. No. 3,29S,367 to Bergman discloses an apparatus for administering parenteral liquids, which includes capillary tubes of different sizes to control liquid flow. U.S. Pat. No. 3,690,318 to Gorsuch discloses a metering assembly including multiple orifices of different sizes. U.S. Pat. No. 3,878,869 to Yamanouchi, et al. discloses a liquid transfusion system for transfusing a small quantity of liquid by means of a capillary flow system. U.S. Pat. No. 3,931,818 to Goldowsky discloses a liquid administration apparatus comprising a system for providing a constant flow of liquid by means of a sump and float chamber. U.S. Pat. No. 4,175,558 to Hess, III, et al. discloses a parenteral liquid administering device which includes a backflow regulator valve.
While there are systems disclosed for aiding the constant supply of liquid to a patient, no passive system has been heretofore developed which will simultaneously regulate volumetrically the flow of liquid to the system while maintaining a proper hydrostatic pressure system, thus assuring a precise volumetric flow of a specific quantity of liquid into the patient's body over long time periods without regard to fluctuations in the patient's blood pressure or other situations which may have an effect on the temporary rate of flow of the liquid into the patient's system.